The present invention relates to droplet ejection apparatus, in particular an inkjet printhead, comprising at least one chamber formed in a body and communicating with droplet liquid supply means and with a respective nozzle formed in a separate nozzle plate, the apparatus further comprising means for effecting ejection of droplets from the nozzle.
As is well known, inkjet printhead operation can be disrupted when the printhead nozzles become blocked with dry ink residue, paper dust and the like. It is well known to keep nozzles clear by wiping the nozzle plate and/or, covering the nozzles (xe2x80x9ccappingxe2x80x9d) and washing the nozzle plate with an appropriate liquid (xe2x80x9cflushingxe2x80x9d) or forcing ink through the nozzles (xe2x80x9cpurgingxe2x80x9d) either by applying a vacuum to the nozzle plate or by applying pressure to the ink supply. The ink emitted during the purging process is typically collected in a cap that seals with the outlet surface of the nozzle plate. The cap may also be placed on the nozzle plate when the printhead is dormant, thereby to reduce the rate at which ink in the nozzles dries out.
The nozzles are typically formed in the nozzle plate by laser ablation, for example by the method described in WO 93/15911 (belonging to the applicant and incorporated herein by reference) and to this end the nozzle plate is generally manufactured from a separate, thin (typically 50 xcexcm) sheet of ablatable material, typically polyimide, polycarbonate, polyester or polyetheretherketone, although, acrylics or non-vitreous inorganic material might also be used.
The nozzle plate is of necessity sealed to the body at the end of the channels, generally by means of adhesive. In addition, the nozzle plate may be extended some way above, below and to either side of the body and the ends of the channels so as to provide a surface of area sufficient to ensure effective sealing of the cap.
It has been found that an extended nozzle plate made of the thin material discussed above requires support at its periphery. It has further been found that the demands placed on the adhesive bond attaching the nozzle plate to such a support differ from those placed on the adhesive bond attaching the nozzle plate to the body in which the ink chambers are formed. In the latter case, the adhesive layer is made as thin as possible consistent with an effective body/nozzle plate seal between adjacent ink chambers, thereby minimising the amount of adhesive that might otherwise flow into and (at least partially) block up the ink chambers. However it has been found that such a thin layer is not sufficiently robust to withstand the forces generated elsewhere on the nozzle plate and particularly at its periphery during the aforementioned capping, wiping and other processes. Of these forces, the peel force generated, for example, by a wiper blade passing over the edge of the nozzle plate, has been found to be the most significant.
It is an object of the present invention to provide a printhead better adapted to the demands of manufacture and operation.
Accordingly, the present invention consists in one aspect in droplet ejection apparatus, comprising a body having at least one droplet liquid chamber; a separate nozzle plate providing a respective nozzle for each droplet chamber, the nozzle plate being bonded to the body by means of a first adhesive layer having a first average thickness; and a nozzle plate support bonded to the nozzle plate by means of a second adhesive layer having a second average thickness greater than said first average thickness.
Preferably, the first and second adhesive layers lie substantially in the same plane.
Suitably, the nozzle plate has an outlet surface containing the outlet of each nozzle and an inlet surface containing the inlet of each nozzle, the body and the nozzle plate support being bonded to the inlet surface of the nozzle plate.
The present invention consists in another aspect in a method of manufacturing droplet ejection apparatus which comprises a body having at least one droplet liquid chamber and a termination plane to which the or each chamber opens; a separate nozzle plate bonded to the termination plane of the body and providing a respective nozzle for each droplet, and a nozzle plate support bonded to the nozzle plate, the method comprising the steps of applying an adhesive layer to the nozzle plate; applying an adhesive layer to the nozzle plate support; aligning the adhesive layer on the nozzle support with the termination plane of the body and contacting the adhesive layer on the nozzle plate with the body and with the adhesive layer on the nozzle support, thereby to produce an adhesive bond layer between the nozzle plate and the nozzle plate support which is thicker than the adhesive bond layer between the nozzle plate and the body.
The use of nozzle plate/support means and nozzle plate/printhead body adhesive layers of differing thickness allows printhead integrity to be maintained during operation without compromising manufacturing quality.
Advantageous embodiments of the invention are set out in the description and dependent claims.